Field of Invention
The present invention relates to electrical tools, and more particularly to rechargeable electrical tools that utilize nickel-zinc battery (system). The present invention further relates to nickel-zinc battery system (battery pack) adapted for electrical tools and manufacturing method therefor.
Description of Related Arts
Electrical tools, especially rechargeable electrical tools, such as electric drill, electric hammer, electric planer, concrete vibrator, electric wrench, electric screwdriver, electric saw, and electric impact drill, usually require rechargeable battery to serve as power supply. Normally, a rechargeable electrical tool has a rechargeable battery (system), an electric motor, a transmission mechanism, and a working portion, such as the drill bit of an electric drill, the hammer of an electric hammer, the planer blade of an electric planer, the vibration output unit of a vibrator, the spanner of an electric wrench, etc. Generally, the battery system of a rechargeable electrical tool provides electric power, such that the electric motor can be started to provide driving force. Then the transmission mechanism transmits the driving force output by the electric motor to the working portion of the electrical tool and drives the working portion so as to implement the corresponding function of the electrical tool.
Nowadays, rechargeable batteries for rechargeable electrical tools are usually nickel-cadmium battery or lithium battery. Nickel-cadmium battery or nickel-cadmium battery system (or nickel-cadmium battery pack) has advantages like repeatable charging and discharging, economical and practical, low internal resistance, rapid charge rate, and ability of providing heavy current for the load. Unfortunately, nickel-cadmium battery has several drawbacks as well. First, both the producing and utilizing of nickel-cadmium battery pollute the environment. Next, the memory effect of nickel-cadmium battery makes its battery capacity decrease rapidly and reduces its duration significantly. Lithium battery or lithium battery system (or lithium battery pack) has higher energy density and high power endurance. However, either external short circuit, internal short circuit, or overcharge of the lithium battery or lithium battery system (or lithium battery pack) can cause fire or explosion of the battery. Hence, for operational safety, a lithium battery or lithium battery pack has to have a protective circuit (PCB) to avoid high temperature and overcharge/over-discharge of the lithium battery or lithium battery system (or lithium battery pack). Also, a lithium battery or lithium battery system (or lithium battery pack) needs low-voltage protection to prevent battery damage caused by its self-discharge. Moreover, the requirements of the operating environment of lithium battery or lithium battery system (or lithium battery pack) are strict. Both high temperature and low temperature environments can lead the battery fail. Nevertheless, electrical tools, especially rechargeable electrical tools, are usually required to be utilized under severe environmental conditions. Lastly, the protective circuit (PCB) of lithium battery or lithium battery system (or lithium battery pack) may not completely avert the security risks of the lithium battery or lithium battery system.